The etiology of most congenital problems remains unrecognized. Progress towards preventing developmental defects will ultimately depend on research directed at understanding basic mechanisms. It is now clear that for a variety of organisms, the critical events of early embryogenesis are dependent upon information synthesized and sequestered during the production of the egg. One source of this information is a large complex pool of gene transcripts. Recently, this laboratory has discovered a small group of mRNAs that are specifically localized to the vegetal pole of frog eggs. Since embryonic determination appears to be mediated by morphogenetic substances specifically localized in the cytoplasm of the egg, it is important to characterize these localized mRNAs and to determine their role in development. Two known determinants, those specifying the germ cell lineages and those specifying the dorsal axial structures, also reside in the vegetal region of the egg. In this proposal experiments are outlined to [1] isolate molecular clones encoding regionally localized maternal mRNAs; [2] determine the developmental history of these localized mRNAs; [3] determine the cellular and subcellular fate of localized maternal mRNAs during normal development and in double axis embryos; [4] determine if the nucleotide sequence of vegetal pole specific gene transcripts contains the information necessary or sufficient for localization. The general strategy involves using polyA+RNA isolated from the animal, middle, and vegetal regions of the Xenopus egg to select for recombinant DNA clones containing localized maternal sequences. These clones will be used in blot and in situ hybridization procedures to follow their developmental fate both quantitatively and at the cellular level. Microinjection of vegetal pole specific transcripts into the animal pole of eggs will yield information concerning the mechanism of message localization. These proposed studies should provide the framework necessary for understanding the role of localized maternal mRNAs in development.